All forms of the valve of the present invention embody an extremely sensitive and reliable check valve utilizing an annular diaphragm element having a relatively large effective area exposed to the pressure of the fluid for controlling a valve having a relatively small sealing area. Thus, miniscule pressure differentials will give relatively high sealing forces. The possible uses for the single-function check valve are virtually unlimited, however it has been found to be ideal in vacuum control systems for automotive heating and air conditioning systems. The multifunction form of the valve of this invention is particularly suited for use in an evaporative emission control system for a motor vehicle having an internal combustion engine. The primary function of evaporative emission control systems is to eliminate or reduce the quantity of undesirable hydrocarbon fuel vapors which evaporate to the atmosphere from the fuel system, usually through the vents which are normally provided. In such an application the valve inlet is connected to the fuel tank, the primary outlet to the engine, either directly or through a cannister of activated charcoal in accordance with known practice, and the secondary outlet to the atmosphere or a secondary receptacle, either directly or through an adsorbing medium in accordance with the present invention. When vapor pressures start to build up in the fuel tank the primary pressure relief section of the present valve, which is responsive to extremely small pressure differentials (i.e. less than 0.2 psig), opens to permit such vapors to accumulate in the engine (crankcase and/or air cleaner) or a charcoal loaded cannister via the primary outlet. This prevents the vapors from going into the atmosphere. In most systems vapors which accumulate when the engine is not running are purged by intake manifold vacuum when the engine is started, so that capacity is recreated for accumulating vapors when the engine is again stopped. In practice it has been found that under certain conditions (extreme heat, etc.) the quantity of vapor evaporating in the fuel tank is so great that the primary system cannot handle them, and a consequence pressure builds up in the fuel tank. This is undesirable because it may rupture the tank or if repeated may cause seams to crack and leak. The secondary pressure relief section of the present valve prevents this by opening when the pressure differential reaches a potentially injurious level to permit such excessive vapors to escape from the tank via the secondary outlet, in addition to the primary outlet. In known systems the secondary outlet communicates directly with the atmosphere, however one aspect of the present invention resides in communicating such excessive vapors to an auxiliary receptacle such as the interior of a box section of the vehicle frame, either directly or via an adsorbing medium disposed either inside or outside the hollow frame section. Should the pressure in the tank ever drop below atmospheric (such as might be due to rapid cooling, action of the fuel pump, etc.) collapsing of the tank and/or flexing cracks are prevented by the check valve function of the present valve which causes it to open in response to an extremely small negative pressure condition (e.g. 1 inch water column) in the tank to place the latter in communication with the atmosphere via the secondary outlet.
The dual-function form of the present valve is also particularly suited for an evaporative emission control system, but one which is less sophisticated than the one described above. In this simpler system, venting of the fuel tank to atmosphere takes place through the cap for the tank filler tube. The valve is disposed in the cap and has a pressure relief function which operates to prevent venting unless the vapor pressure in the tank exceeds atmospheric by some predetermined value (high enough to eliminate most unnecessary venting, but low enough to prevent pressure damage to the tank or fuel system). It also has a check valve function which is responsive to the existence of even an extremely small negative pressure in the tank to place it in communication with the atmosphere, as does the multifunction valve. Another aspect of this invention concerns the provision of an inproved gas cap construction having improved sealing means.
Primary objects of the present invention reside in the provision of a family of relatively simple and inexpensive valves having the aforesaid characteristics and functions, which valves are responsive to extremely small positive or negative pressure differentials and yet remain fully and reliably closed until conditions call for opening.
Another important object of the present invention concerns the provision of a family of very sensitive diaphragm type valves which will close without pressure reversal and which incorporate means preventing overstressing or extrusion of the diaphragm itself.
Another important object of the present invention resides in the provision of a very sensitive check valve which will open in response to extremely small pressure differentials, in the order of several inches of water, and yet which will not leak when subjected to relatively large pressure reversals, in the order of one atmosphere or more.
Another important object of the present invention resides in the provision of a multifunction valve in which the primary and secondary pressure relief functions are accomplished by essentially two relief valves in series, whereby the secondary valve remains fully closed until the primary valve is fully open, and one which is not responsive to pressures downstream of the primary outlet.
Another important object of the present invention resides in the provision of an evaporative emission control system in which secondary vapors are not communicated directly to the atmosphere.
Another important object of the present invention resides in the provision of an extremely simple and inexpensive technique for mounting to a motor vehicle such a valve for an evaporative emission control system.
Another important object of the present invention resides in the provision of extremely simple and highly efficient sealing means for valves.
Another important object of the present invention resides in the provision of a very sensitive dual function valve of the type described which will fit within a conventional fuel tank filler tube cap.
Another important object of the present invention resides in the provision of a fuel tank filler tube cap having improved sealing means.
Other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.